Comprehensive Notes on Locomotion and Movement Class 11 Biology | NCERT Chapter Summary, Important Concepts, and Muscle Types Explained

Locomotion and Movement – Class 11 NCERT Detailed Explanation

Introduction

Living organisms exhibit a wide range of activities that help them survive, adapt, and interact with their environment. Movement is one such vital activity. It refers to any visible change in the position of any part of an organism. Locomotion, on the other hand, is the movement of the entire organism from one place to another.

All locomotions are movements, but all movements are not locomotion.

For example, the movement of eyelids or the contraction of heart muscles are movements, while walking, running, or swimming are locomotions

Types of Movement

Movements in the human body can be classified into three main types:

1. Amoeboid Movement

Found in cells such as leukocytes (white blood cells).

Involves cytoplasmic streaming and pseudopodia formation.

Example: Movement of macrophages during infection.

2. Ciliary Movement

Occurs due to coordinated beating of cilia.

Found in respiratory tract and reproductive tracts.

Example: Movement of ova in fallopian tubes.

3. Muscular Movement

Most common in higher animals including humans.

Due to contraction and relaxation of muscle fibers.

Responsible for locomotion, facial expressions, and voluntary activities.

Muscles and Their Types

Muscles are specialized tissues responsible for producing force and movement. They constitute about 40–50% of body weight.

1. Skeletal Muscles

Also known as striated muscles.

Attached to bones and under voluntary control.

Show light and dark bands (striations).

Function: locomotion, posture maintenance, facial expressions.

2. Smooth Muscles

Non-striated, involuntary muscles found in walls of internal organs.

Example: stomach, intestines, urinary bladder.

Responsible for involuntary activities like peristalsis.

3. Cardiac Muscles

Found only in the heart.

Striated but involuntary.

Interconnected by intercalated discs for synchronized contraction.

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Structure of a Skeletal Muscle

Each muscle consists of bundles of muscle fibers enclosed in a sheath called epimysium.

Each muscle fiber is:

Long, cylindrical, multinucleated.

Enclosed by sarcolemma (plasma membrane).

Contains sarcoplasm (cytoplasm), sarcoplasmic reticulum, and myofibrils.

Myofibrils contain two types of contractile proteins:

Actin (thin filament)

Myosin (thick filament)

These filaments form sarcomeres, the structural and functional units of muscle contraction.

Mechanism of Muscle Contraction

Described by the Sliding Filament Theory:

Discovered by Huxley and Niedergerke.

During contraction:

Actin filaments slide inward over myosin filaments.

The sarcomere shortens, causing muscle contraction.

Energy for contraction comes from ATP.

Steps:

1. Nerve impulse reaches the muscle fiber.

2. Calcium ions are released from sarcoplasmic reticulum.

3. Calcium binds to troponin, exposing active sites on actin.

4. Myosin heads form cross-bridges with actin.

5. ATP hydrolysis provides energy to pull actin filaments inward.

6. Muscle relaxes when calcium ions return to the sarcoplasmic reticulum.

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Skeletal System

The human skeleton provides shape, support, and protection. It consists of 206 bones in adults.

1. Axial Skeleton – 80 bones

Skull, vertebral column, ribs, sternum.

2. Appendicular Skeleton – 126 bones

Limbs and girdles.

Functions:

Protection of organs (skull protects brain, ribs protect heart/lungs)

Locomotion (with the help of muscles)

Hematopoiesis (formation of blood cells in bone marrow)

L

A joint is a point of contact between two bones or between bone and cartilage.

Types of Joints

1. Fibrous Joints (Immovable) – e.g., skull sutures

2. Cartilaginous Joints (Slightly Movable) – e.g., vertebral column

3. Synovial Joints (Freely Movable) – e.g., knee, elbow, shoulder

Synovial Joints have:

Synovial fluid (lubrication)

Articular cartilage (reduces friction)

Ligaments (hold bones together)

Disorders of Muscular and Skeletal System

1. Myasthenia Gravis – Autoimmune disease causing muscle weakness.

2. Muscular Dystrophy – Genetic disorder leading to progressive muscle degeneration.

3. Arthritis – Inflammation of joints.

4. Osteoporosis – Decrease in bone density, common in elderly.

5. Gout – Uric acid crystal deposition in joints causing pain.

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